Viscosity Lesson for Kids

Instructor: Josh Corbat

Josh has taught Earth Science and Physical Science at the High School level and holds a Master of Education degree from UNC-Chapel Hill.

Have you ever wondered why some liquids flow faster than others? In this lesson, we will learn about the property of viscosity, which explains why some liquids flow fast and others flow slowly. Then you can test your understanding with a short quiz.

What Makes a Liquid Flow?

Have you ever thought of peanut butter as a liquid? If you smear peanut butter on a wall (not recommended) it will slowly slide or flow downward. If you spray water on a wall, though (still not recommended), it will flow down the wall very quickly. What makes this happen?

Peanut butter, which is actually a liquid, flows very slowly
Peanut butter

Gravity is a force on Earth that makes everything fall downward. Actually, downward is different in different parts of the world. Think of a globe. If you are at home, and you look at a place on the other side of the globe, down points in a different direction, right? A better definition of the downward pull of gravity is that everything is pulled toward the center of the Earth. Gravity is what makes liquids flow. Without gravity (like in space) liquids would just float around. (This would be fun to see, but would make taking a shower or bath pretty hard).

Gravity pulls everything that is about the same size with about the same amount of force. Peanut butter, honey, motor oil, and water all flow at different rates. Why is that? Well, the answer is that they each have a different viscosity. Let's see what that means.

What is Viscosity?

Viscosity is the property of a liquid that describes how fast or slowly it will flow. You can think of viscosity as how thick a liquid is. A liquid with high viscosity - that is thick, like peanut butter - will flow slowly. A liquid with low viscosity, or that's thin, like water, will flow quickly (in other words, it will flow freely). The next section will give a few examples, but take a minute to think about these four liquids: peanut butter, water, honey, and motor oil. Can you figure out which have a high viscosity and which have a low viscosity? Can you put them in order from high viscosity to low viscosity?

Examples of Liquids and Their Viscosities

Of the four liquids listed in the last section, peanut butter is the thickest - and it has the highest viscosity, because it will flow the slowest. In fact, some people don't even realize peanut butter is a liquid because it looks like it's not flowing at all - but it is - just very slowly.

Honey is next in line, because it has a high viscosity but not as high as peanut butter. If you dip a spoon in honey and lift it up, it flows in blobs and is runny. Honey and peanut butter are good liquids to use as examples when you think about a liquid's viscosity, or thickness.

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